Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch panels, joysticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch panel, which can be a clear panel with a touch-sensitive surface. The touch panel can be positioned in front of a display screen so that the touch-sensitive surface covers the viewable area of the display screen. Touch screens can allow a user to make selections and move a cursor by simply touching the display screen via a finger or stylus. In general, the touch screen can recognize the touch and position of the touch on the display screen, and the computing system can interpret the touch and thereafter perform an action based on the touch event (the touching of fingers or other objects upon a touch-sensitive surface).
Touch panels can include an array of touch sensors capable of detecting touch events. Some touch panels may be able to detect multiple touches (the touching of fingers or other objects upon a touch-sensitive surface at distinct locations at about the same time) and near touches (fingers or other objects within the near-field detection capabilities of their touch sensors), and identify and track their locations. Examples of multi-touch panels are described in Applicant's co-pending U.S. application Ser. No. 10/842,862 entitled “Multipoint Touchscreen,” filed on May 6, 2004 and published as U.S. Published Application No. 2006/0097991 on May 11, 2006, the contents of which are incorporated by reference herein.
Virtually all portable devices rely on electrical power in one form or another. Some of them rely on various types of batteries which store energy in chemical forms. Some batteries are disposable and they produce only a certain fixed amount of electrical power from the stored energy. Some batteries, such as nickel-cadmium NiMH (Nickel Metal Hydride) or lithium-ion batteries, may be recharged, but they also generate only a finite amount of electrical energy between recharges. For devices such as portable music players, when they are in continual use, they can be used for about 10 or 20 hours, or often much less, before their batteries need to be replaced or recharged.
Using solar cells on portable devices, particularly handheld portable devices with small form factors, however, poses certain technical and/or design problems. For example, the small size of the portable device means there is a small surface area which can be used for placing solar cells. This surface area is typically further reduced by other components that appear on the surfaces of the devices such as input devices and display devices. Since the maximum solar energy that can be produced from a solar panel is roughly proportional to the surface area of the solar cells, this reduces the amount of solar energy that may be gained from the solar panel.
FIG. 1 shows a handheld calculator 102 with a built-in solar cell 104. The solar cell or solar panel 104 is embedded on the front of the device. The calculator includes a display 106 and an area for user input, which comprises multiple keys 108. It should be noted that the upper area of the device used for the solar panel could have been used for other purposes, for example, for a bigger display or input area. Alternatively, the overall size of the device could have been reduced were it not for the solar panel.